1. Field
The presently disclosed embodiment relates to a method and a device for monitoring the dynamic confinement of a confinement enclosure that is at a raised or at a reduced pressure in relation to the exterior surroundings. The presently disclosed embodiment also relates to an enclosure equipped with such a confinement control device.
2. Brief Description of Related Developments
It is known practice within the nuclear industry to use a confinement enclosure in order to clean up and/or to dismantle radioactive equipment of a nuclear installation, for example if this equipment has become obsolete or if the installation itself is being shut down.
FIG. 1 shows such a confinement enclosure 1 of the prior art. This confinement enclosure 1 comprises a set of vinyl air locks comprising a personnel entrance and exit air lock 2, a materials entrance and exit air lock 3 and an intervention air lock 4. It is inside this latter air lock 4 that one or more operators carry out the operations of cleaning up and/or of dismantling the contaminated equipment.
The first two air locks 2, 3 each have access to the exterior and direct access to the intervention air lock 4. These two air locks 2, 3 do not communicate with one another such that the first air lock 2 is reserved exclusively for personnel, the second air lock 3 being intended only for the removal of the materials resulting for example from the dismantling of the radioactive equipment.
Each air lock 2-4 is typically formed of a metal structure with flexible vinyl walls. Access to the air locks 2-4 is had via two vinyl sheets 5.
These vinyl walls prevent contaminated substances from being dispersed into the environment during cleanup operations.
Such a confinement enclosure 1 intended for dismantling and/or cleanup operations is kept at a reduced pressure in relation to the host space in which this enclosure is situated by means of a ventilation system which may be autonomous or may be connected to the network that exists within the host space.
The materials and personnel entrance/exit air locks 2, 3 are ventilated by air transfer. Only the intervention air lock 4 has forced air extraction (not depicted).
During cleanup and/or dismantling operations, the air flows through the intervention air lock 4 are extracted by a fan preceded by high efficiency particulate air filters (HEPA filters) capable of trapping the particles carried in the air thus extracted.
This creation of a reduced pressure therefore allows contaminated dust generated for example when cutting up radioactive equipment to be confined and sucked up.
The safety of operations relies on the combination of static confinement (airtightness of the walls) of the confinement enclosure and dynamic confinement (ventilation) that allows this enclosure to be kept at a reduced pressure.
The French Nuclear Safety Authority (ASN) recommends that such a confinement enclosure be kept at a reduced pressure by maintaining a pressure differential of the order of −40 Pa to −80 Pa with respect to the host space.
This reduced pressure is currently measured at the start of each working shift, but it is not possible from this to deduce with certainty that this level of reduced pressure is being maintained throughout the cleanup operations and/or the operations of dismantling contaminated material.
Specifically, this reduced pressure may, for example, vary suddenly as a result of a break in the static confinement or alternatively as a result of the filtration system becoming plugged, leading to a drop in the extraction flow rate.
When this happens, the amount of reduced pressure no longer falls within the range of recommended values, causing the cleanup work and/or dismantling work to have to stop until the target reduced pressure can be re-established.
Now, such work stoppages lead to additional costs and significant extensions of deadlines which are incompatible with the economic requirements of the companies involved.
Conversely, there are confinement enclosures which require a raised pressure in order to keep the dust outside such an enclosure. Maintaining a raised pressure makes it possible to maintain a healthy atmosphere inside the enclosure, namely an atmosphere that is devoid of the kind of dust that would hamper the operations performed in this enclosure.
The safety of operations relies on the combination of static confinement (airtightness of the walls) of the confinement enclosure and dynamic confinement (ventilation) that allows this enclosure to be kept at a raised pressure.
The presently disclosed embodiment seeks to alleviate these various disadvantages by proposing a method and a device for monitoring the confinement of an enclosure that is at a reduced pressure or at a raised pressure in relation to the exterior surroundings in which this enclosure is placed, being simple in their design and mode of operation and guaranteeing that these operations can be carried out safely.
Another object of the presently disclosed embodiment is such a method and such a device for monitoring the dynamic confinement of an enclosure that makes it possible to continuously monitor the quality of the dynamic confinement of this enclosure.
In the remainder of this document, the term “confinement” will refer to dynamic confinement or containment. The term “enclosure” will refer to a confinement space.